The invention relates to a method of an to a machine for making rod-like fillers of fibrous material, such as natural, reconstituted or substitute tobacco or filter material for tobacco smoke. More particularly, the invention relates to improvements in a method of and in an apparatus for making rod-shaped fillers of fibrous material which is supplied to one side of an air-permeable conveyor whereon the fibrous material forms a continuous stream which contains a surplus and is advanced past a trimming or equalizing device which removes the surplus so that the thus trimmed or equalized stream constitutes a rod-shaped filler which is ready for draping into a web of cigarette paper or other suitable draping material so as to form a continuous cigarette, cigarillo, cigar or filter rod.
It is well known to build a continuous stream of fibrous material along one side, particularly along the underside, of an endless air-permeable belt conveyor while the other side of the conveyor is acted upon by suction so that the fibrous material is attracted to and advances with the conveyor in the desired direction, namely toward and past the trimming device prior to entering the draping station where the filler is converted into a rod. The surplus removing or trimming device can comprise one or more rotary disc-shaped members which grip the particles of fibrous material at a selected distance from the underside of the conveyor, and a brush or a milling tool which segregates the fibrous material beneath the disc or discs from the major part of the stream.
U.S. Pat. No. 3,731,693 discloses a rod making machine wherein the density of the filler is influenced by monitoring the density of the filler and by regulating suction which is applied to attract the stream of unequalized fibrous material to the air-permeable conveyor. This renders it possible to mount the trimming device at a fixed distance from the conveyor so that the machine can operate properly, namely produce a filler of desired density, without relying on complex and expensive means for moving the trimming device relative to the conveyor.
U.S. Pat. No. 4,574,816 discloses a machine wherein the trimming device is installed at a fixed distance from the air-permeable conveyor and the density of the filler is regulated by varying the rate of admission of fibrous material into the stream building zone in dependency upon the intensity and/or other characteristics of signals which are transmitted by a device serving to monitor the density of the trimmed stream. The rate of admission of fibrous material is increased when the density of the filler is too low, and the rate of admission of fibrous material is reduced when the monitored density is excessive. It was further proposed to additionally regulate suction in the chamber which serves to attract the stream to the air-permeable conveyor, namely to regulate suction in dependency upon the changes of intensity and/or other characteristics of signals from the density monitoring device so that suction is increased (i.e., the pressure in the suction chamber is reduced) when the density of the filler is too low, and vice versa.
U.S. Pat. No. 3,750,675 discloses a machine which is analogous to that of the aforementioned U.S. Pat. No. 3,731,693. Thus, the position of the trimming device remains unchanged but suction which is applied to attract the stream of fibrous material to the foraminous conveyor is regulated in dependency upon the characteristics of signals which are generated by a density or mass monitoring device.
U.S. Pat. No. 4,306,573 discloses a machine wherein the trimming device is movable relative to the air-permeable conveyor in dependency upon signals which denote variations of resistance of the rod-shaped filler to the flow of a gaseous fluid therethrough.
British Pat. No. 2,133,967 discloses a machine wherein the trimming device is fixed relative to the air permeable conveyor and the density monitoring device transmits signals which are utilized to regulate the speed of the conveyor so as to maintain the density of the filler at a constant value.